The disclosed invention relates to a method and at least one apparatus for plugging fluid or slurry pipe lines preparatory to making repairs or testing new pipe line installations at selected precise locations.
Many fluids, liquids, and suspended particles or slurries are now transported through pipe lines, such as crude oil, lubricating oil, natural gas, gasoline, and other marketable gases, liquids, and slurries from one area to another. These pipe lines are often of considerably length and over various geographic terrains.
Because of the considerable cost of pipe fittings, as large diameter valves, it is not economical to provide valves every mile or so in pipe lines, but instead, pipe lines may extend for many miles between valves. Accordingly, in the event of damage to a pipe line or the occurrence of the need for modification or structural change to a pipe line at a given point, a very serious problem arises as to the manner in which the flow of liquid through the pipe line is to be controlled during repair or alteration.
If a break occurs in the center of a fifty mile pipe line that could be temporarily repaired such that flow could be resumed, even at reduced flow rates, or a need arises for modifying the pipe line at this point, it would be completely infeasible to use the existing valves for isolating this section of the pipe line due to the tremendous quantity of fluid therein. If the pipe line were full of crude petroleum, the least valuable liquid likely to be passing through the pipe line, there would still be a body of liquid of tremendous value contained within such a section of pipe, and the economic loss of discarding this liquid and the damage to the ecology could not be tolerated even if a suitable location of disposal could be found. Draining of this section of pipe into tanks, tank cars, or tank trucks, or other portable means or displacing the line with nonpollutants such as nitrogen or water would be very expensive and not very practical. Thus, repair or modification of the pipe line under these conditions, while not impossible, would be a lengthy, time consuming, and expensive operation.
One method to repair pipe lines is thus to evacuate and isolate a section of pipe line by using two internally transportable plugging devices or pigs, some type of means for initially stopping the pair, locating one pig at the upstream terminus of the section to be isolated, and locating the second pig at the downstream terminus of the pipe section isolated. Here the pigs are expanded to seal off the pipe section, with or without flow being maintained through a bypass, the section evacuated, repaired, refilled, and the pigs released and recovered.
While such apparatus are used, all contain various certain objectionable features and the instant invention overcomes such objections. There are those types of pigs utilizing rack and gears for expanding thereof as disclosed in U.S. Pat. No. 2,786,489, but such mechanisms get complicated, are expensive to purchase and maintain, and are of low efficiency. Others have projections into the pipe to contact and expand the pig as disclosed in U.S. Pat. Nos. 2,339,544, 2,929,410, 3,040,779, and 3,285,290. Other pigs responsive to only one signal are disclosed in U.S. Pat. Nos. 3,298,399; 3,381,714; 3,401,720; 3,483,895; 3,690,348 and 3,837,214. Another system utilizes a large expensive full encirclement fitting for being welded on the line. This "one shot" attachment to a high pressure pipe line must be coated and cathodically protected, as well as physically protected, during the life of the parent facility. Another system involves a sophisticated series of fittings for being welded on the line in order to trap and lock two hydraulically expandable pigs into position. The usual and most common method deemed to be used to cease flow in a pipe line temporarily is the utilization of the T. D. Williamson "Stopple" plugging systen which comprises boring a large hole at each of the two extremities of the pipe section to be worked on, inserting a plug in each large hole and pivoting the plug about a transverse axis to plug-up the pipe, and after the repair work is done, the plugs are pivoted back and removed from the holes, and large permanent flanges secured over the holes. Even after the pipe section is repaired in the above cases, the series of fittings remain on the line and must be protected against physical or cathodic damage as in the above described system.